Apparatus for flat plate powder gravure printing



May 13, 1969 D.-ISMITH ETAL 3,443,515

APPARATUS FOR FLAT PLATE POWDER GRAVURE PRINTING Filed Aug. 5, 19663,443,515 APPARATUS FOR FLAT PLATE POWDER GRAVURE PRINTING Daniel Smith,Riverdale, N.Y., and Norman S. Cassel,

Ridgewood, N.J., assignors to Interchemical Corporation, New York, N.Y.,a corporation of Ohio Filed Aug. 3, 1966, Ser. No. 570,004 Int. Cl. B41b19/00 US. Cl. 101-150 12 Claims ABSTRACT OF THE DISCLOSURE Anelectrostatic powder gravure printing apparatus where the gravureengraving is on a flat circular rotatable plate in operable proximity toa powder supplier, a doctoring device, an electrostatic charging means,and a device for bringing the substrate to be printed on close to thepowdered engraving, the device being furnished with means forestablishing an electrical field between the charged powder and thesubstrate. Frustums of cones and also cylinders may be the substrates.

This invention relates to gravure printing with the aid of electrostaticforces using dry powder as printing material. More particularly, itrelates to novel apparatus for flat plate powder gravure printing.

Copending application S.N. 372,226, Reif et al., filed June 3, 1964, nowPatent 3,296,965 issued Jan. 10, 1967, is a basic application in thefield of powder gravure printing and is directed primarily to gravureprinting with printing cylinders.

Gravure printing has the advantages of being elfective on a wideassortment of substrates and of producing high quality prints. Powderhas the advantage over conventional links of eliminating organicsolvents with their attendant odors and fire hazards. Powde-r alsopermits the use of insoluble resins as well as soluble ones. Employingelectrical fields for printing eliminates the need for actual contactbetween the substrate and the printing plate. Printing can beaccomplished even when the printing plate is as much as 0.1 inch fromthe surface to be printed on. It is also possible to do contact printingelectrostatically. By powder gravure, prints may be effectively made onquite irregular surfaces and also on materials where contact wouldinjure the material or the printing plate. For example, prints can bemade on wet substrates. The powder gravure process has the advantageover other powder printing processes of a built-in metering system. Thatis, each cell of the gravure printing element provides the same amountof powder for each print made on the substrate from that cell, thusproviding uniformly printed reproductions.

The process is conveniently carried out by depositing a suitableprinting powder in the cells of a gravure printing element, the powderbeing substantially free from elec trostatic charges, applying anelectrostatic charge of substantial magnitude to the powder in thecells, transferring the charged powder to a substrate in an electricfield of appropriate direction, and optionally fixing the powder thustransferred to the substrate. The magnitude of the charges required andmeans for imparting them are well known to the art, as is the process offixing resinous powders to substrates. The powders can be charged, forexample, by induction if they are sufficiently conductive. On the otherhand, if the powders are good insulators they can be charged by ionbombardment from a corona. Electrical fields can be established onconductive surfaces by direct application of potential, and on thesurfaces of insulating materials by the deposition of charges.

On certain structures, particularly frustums of cones,

nited States Patent O 3,443,515 Patented May 13, 1969 p ce difficultieshave been encountered in printing by using a printing cylinder. In orderto overcome these ditficulties, we have developed novel apparatus forcontinuous printmg by powder gravure using a flat gravure plate.

The novel apparatus of this invention comprises a fiat circular gravureplate. The flat surface of this plate has formed therein a gravure typeengraving. The plate, or at least the annular portion of the platecontaining the engraving, is rotatable about the axes of the plate. Asthe engravmg rotates it moves past the following components 'WhlCh areoperatively associated with the plate and are in fixed positions alongthe path of rotation of the engrav- 1ngs: means for depositing achargeable dry powder on the engraving including means for removing theexcess powder; electrostatic charging means for charging the depositedpowder; means for bringing the substrate to be printed upon into closeproximity with the engraving and means for establishing an electricalfield between the charged powder and the substrate which is brought intoproximity with the engraving. The field thus established causes themovement of the powder from the engraving and the deposition of thepowder on the substrate in the same pattern as the engraving.

In the most advantageous embodiments of the apparatus of this invention,the means for bringing the substrate into proximity with the engravingare means which will rotate a solid of revolution such as cylinder, coneor frustum thereof so that the curved surface of the solid is in closeproximity to, even in contact with, the engraving and is preferablymoving substantially in the same direction as the engraving at the pointclosest to the engraving.

It should be noted that if the surface to be printed upon is made of arelatively dielectric material such as plastic, wood, glass or paper,the substrate is preferably but not necessarily in contact with theengraving. On the other hand, if the surface to be printed upon is anon-dielectric or conductive material such as metal, the surface shouldbe separated from the plate by an air space.

FIG. 1 shows one preferred embodiment of the present invention. Flatcircular gravure plate 10 comprises stationary center portion 11 androtatable annular ring 12 which moves in the direction shown andcontains one or more gravure engravings, in this case three engravings13, 14 and 15. As the engravings pass under powder reservoir 16 which isfixed in the position shown-this reservoir is of the same type describedin copending application S.N. 372,226-chargeable powder from a dischargeoutlet in the base of the reservoir is deposited into the gravureengraving. Doctor blade 17 removes the excess powder from the surface ofthe rotating portion of the plate. One conventional method ofaccomplishing the removal of powder from the surface involves apertures18 which trail the moving engravings. Excess powder which is scrapedfrom the surface by doctor blade 17 is swept into an aperture 18 by theblade. The gravure engraving carrying the chargeable powder then passesunder the corona discharge produced by corona wire 19 whereby a chargeis applied to the particles. The engraving carrying the chargedparticles then passes under the substrate to be printed upon which inthis case is a plastic container in the form of a frustum 20.Thecontainer is mounted on a rotating mandrel 21 of a conductive material.The container 20 rotates in or near tangential contact with theengraving. At or near the point of contact, the container is moving inthe same direction as the engraving and is preferably but notnecessarily moving at the same speed as the engraving. An electricalfield is established between the mandrel 21 and the annular portion ofthe plate 12 by applying an electrical potential difference betweenthese two elements. The resulting field which passes through dielectriccontainer 20 is of such a nature that the charged particles in the 3engraving will tend to move from annular"'plate 12 to mandrel 21.

The particles will of course be intercepted by the surface of theintervening container 20 and be deposited on said surface in a patterncorresponding to that of the engraving. The particles deposited on thesurface of the container may then be fixed to the surface byconventional means such as heating. The container is then removed fromthe mandrel by any conventional automatic means. A fresh container isplaced on the mandrel and awaits the passage of the next engraving. Whenthe container to be printed on is a frustrum of a cone as shown in FIG.1, the container is preferably in tangential contact with the plate andso positioned that the apex of the cone from which the frustum isderived coincides with the center of the circular gravure plate. (Theoutline of the cone is shown in FIG. 1 by dashed lines 23.) When thecontainer to be printed upon is thus positioned, in order to produce atrue representation of the design to be printed on the container, thedesign in the engraving is situated along polar coordinates the radicallines of which pass through the center of the circular plate.

FIG. 2 represents another embodiment of the present invention which isparticularly suitable for printing on cylindrical substrates such ascans or bottle 30. The elements which are shown diagrammatically mayhave structures similar to those in FIG. 1. Flat circular gravure plate31 contains one or more gravure engravings 32 situated circularly aboutcenter 33 equally distant from center 33 and from each other. The plateis rotated in the direction shown at intervals which may be determinedby dividing 360 by the number of engravings. Since in the presentembodiment there are four engravings, the plate is rotated for intervalsof 90 each. As the engravings pass under powder reservoir 34 and doctorblade 35 powder is deposited in the engraving in the manner describedwith respect to FIG. 1. The engravings filled with powder subsequentlypass under corona discharge wire 36 whereby a charge is imparted to thepowder particles carried in the engraving.

Cylinder bearing mandrel 37 is so positioned with respect to theengravings that after rotation of the plate for an interval which inthis case is 90", the engraving to be printed on the curved surface isaligned parallel to the ends of the cylinder. Mandrel 37 is then somoved that cylinder 30 rolls over engraving 32, the lateral directionsof the roll being parallel to the ends of the cylinder while therotational element of the roll is conventional as shown in FIG. 2. Whilethe bottle is being rolled over engraving 32 the engraving remainsstationary. As in FIG. 1, if container 30 is made of a dielectricmaterial such as glass, the cylinder is preferably in contact with theengraving. On the other hand, if the cylinder is made of conductivematerial, such as metal then it must be spaced from the engraving as itrolls over it. In any event, a potential difference is applied by themandrel 37 and engraving 32 to create an electrical field between themandrel and the engraving of such a nature that the charged particles inthe engraving will move towards the mandrel and consequently bedeposited on the surface of cylinder 30. The transferred powder may thenbe fixed to the cylinder. The cylinder is then removed and a freshcylinder is deposited while the mandrel is moved back to its startingposition. At the same time, the plate may be turned for another 90interval to place the next engraving in printing position.

The powder application means used in the present invention including thedoctoring and brush means are preferably those described in copendingapplication S.N. 372,- 226. The engraved patterns on the printing platesmay represent a variety of structures including various sizes of dots,lines and recessed designs. They may be of course of varying depths.

Although the process of this invention is not limited to the use of anyparticular powder material, the preferred printing powder incombinations of resinous material with colorants dispersed therein asdescribed in copending application S.N. 372,226 may be used. Examplesare Pliolite VTL containing 30% carbon black, Dow PS-2 with 30% carbonblack, a mixture of Dow PS3 and Pliolite VTL in the proportions 3:2together with U1- trasil and colorant.

The resins and colorants were ground in a Mikro Atomizer. Finer grindswere obtained by regrinding the material in a fluid-energy Micronizer.Coarser grinds were obtained by screening a coarse precrush throughZOO-mesh and 325-mesh sieves 74 and 44 microns. There were thus obtainedfractions with mean-mass sizes of 8 and 14 microns with Pliolite VTL"and mean-mass sizes of 4, 11, 18 and 42 microns with Dow PS-2. Pigmentwas milled into the resin before grinding.

Powders with mean-mass size of about 11 to 18 microns are preferred.Finer powder does not fill the printing cells as well and transfers lessreadily. Powders coarser than about 11 to 18 microns mean-mass sizeproduce somewhat grainy prints.

Suitable resins for the process were numerous. Some performed betterthan others but it was found that the use of release agents improved theperformance of many powders in cases where the transfers were otherwisenot as clean as desired. Some of those resins found suitable were ethylcellulose, Durez 19591, Piccolastie D-150, Pliolite S5E, Pliolite VTL,Saran F-120, Tylac CZ 210-4, Vinylite VYI-IH, Vinylite VYNS-B, Dow PS2,(polystyrene), Epon 1004, Lucite 41, Saran F-220, Vinylite VYLF, andGelvatol 40-10.

Pliolite VTL is a vinyl-toluene/butadiene resin.

Dow PS-2 is polystyrene.

Ultrasil is very finely divided silica.

Piccolastic D-150 is a polystyrene resin.

Pliolite S-SE is a copolymer of 1 part by weight of butadiene and 6parts by weight of styrene.

Saran F-120 is a copolymer of vinylidene chloride and acrylonitrile.

Vinylite VYHH is a copolymer of 87% by weight of vinyl chloride and 13%by weight of vinyl acetate. Vinylite VYNS-S is a copolymer of 90% byweight of vinyl chloride and 10% by weight of vinyl acetate. Epon 1004is an epichlorohydrin/bisphenol A type solid epoxy resin having anepoxide equivalent of about 8751025 and a melting point of about -105 C.Lucite 41 is polymethylmethacrylate. Saran F-200 is a vinylidenechloride/acrylonitrile copolymer. Vinylite VYLF is a copolymer of 87% byweight of vinyl chloride and 13% by weight of vinyl acetate. Gelvatol40-10 is a polyvinyl alcohol with 37-42% of residual polyvinyl acetate.

The substrates may be paper, wood, glass, cloth, rubber, plastics,ceramics as well as conductive material such as aluminum foil, metalsheets, tin plate.

While there have been described what is at present considered to be thepreferred embodiments of this invention, it will be obvious to thoseskilled in the art that various changes and modifications may be madetherein without departing from the invention, and it is, therefore,aimed to cover all such changes and modifications as fall within thetrue spirit and scope of the invention.

We claim:

1. A printing apparatus for gravure printing wherein an image is formedon a substrate with a dry printing powder which comprises (a) a flatcircular gravure plate having a fiat surface with at least onegravure-type engraving thereon, said plate and the engraving thereonbeing rotatable about the axis of the plate, and the followingcomponents in fixed positions along the path of rotation of saidengraving: (b) means for depositing a chargeable dry printing powder onthe engraving (c) electrostatic charging means for charging the powderdeposited on the engraving (d) means for bringing a substrate into closeproximity with said engraving (e) means for establishing an electricfield between the charged powder and the substrate when the latter isbrought into close proximity to the engraving to cause the movement ofthe powder from the engraving to the substrate.

2. The apparatus of claim 1 wherein the means for bringing the substrateinto close proximity with the engraving are means for rotating a solidof revolution so that the surface of said solid which is in closeproximity to the engraving is moving substantially in the same directionas the engraving.

3. The apparatus of claim 2 wherein the solid of revolution is acylinder.

4. The apparatus of claim 2 wherein said solid of revolution is a cone.

5. The apparatus of claim 4 wherein the solid of revolution is a frustumof a right circular cone.

6. The apparatus of claim 5 wherein said frustum is made of a dielectricmaterial.

7. The apparatus of claim 6 wherein said frustum is rotated with itscurved surface in tangential contact with said engraving and is sopositioned that the apex of the cone from which the frustum is derivedwould pass through the center of the surface of the circular gravureplate.

8. The apparatus of claim 1 wherein said means for depositing achargeable dry printing powder to the engraving comprise a powderreservoir having a discharge outlet above the plate in combination withdoctoring means in contact with the surface of the engraving positionedalong the path of rotation of the engraving just subsequent to thereservoir.

9. The apparatus of claim 1 further including means for fixing thetransferred powder to the substrate.

10. The apparatus of claim 1 wherein said engraving is on an annularportion of the circular plate, said annular portion being rotatableabout said axis.

11. The apparatus of claim 1 wherein the means for bringing thesubstrate into proximity with the engraving are means for rolling asolid of revolution over the engraving and the engraving is rotatable toa position adjacent to the solid of revolution at which position theengraving remains stationary while the solid is rolled over it.

12. The apparatus of claim 11 wherein the solid of revolution is acylinder.

References Cited UNITED STATES PATENTS 2,787,556 4/ 1957 Hoas. 3,241,4833/1966 Dutf 101-114 3,245,341 4/1966 Childress et al 10 1-150 3,253,5405/1966 Lusher 101-170 3,285,168 11/1966 Childress 101-150 3,296,9651/1967 Reif et al. 101-170 3,302,579 2/1967 Edwards et al. 101-1143,302,580 2/1967 Edwards et al. 101-114 EDGAR S. BURR, Primary Examiner.

US. Cl. X.R. 101-170

